Merocyanines: polyene polymethine transition in donor acceptor-substituted stilbenes and polyenes

摘要: Three series of donor–acceptor-substituted conjugated compounds, namely, stilbenes, the open-chain polyenes equivalent length, and species intermediate structure (polyenes terminated with only one phenyl ring) have been studied by AM1 HMO methods to elucidate compare structural prerequisites ideal polymethinic state (‘‘cyanine limit’’). The transition from polyenic properties has traced in terms bond-length (bond-order) alternation using variation terminal donor acceptor substituents. Stilbenes manifest themselves as notably ‘‘retarded’’ since a larger electronic asymmetry is necessary for them reach same degree character. ground excited shown differ much more strongly stilbenes than respect position bond equalization point on scale donor–acceptor difference. For compounds containing ring, features revealed are between polyenes. large S0–S1 discrepancy general property aromatic ring-terminated chains (stilbenes) related influence character which can be quantified this way. In context, most relevant definition cyanine limit (based invariance upon excitation) was selected existing definitions. major trends polyenic/polymethinic behaviour molecules interpreted topological basis within or even simpler models some additional due interelectronic repulsion taken into account treatment. 2003 Elsevier Science B.V. All rights reserved.